Electron beam image processing device

ABSTRACT

A device containing and providing selection between a plurality of electron beam processing units is located in the vacuum chamber of a microscope, so that the latter can be used in a wide variety of applications without breaking the vacuum.

United States Patent [1 1 Heinemann 1 ELECTRON BEAM IMAGE PROCESSINGDEVICE [75] Inventor: Klaus Heinemann, Sunnyvale, Calif.

[73] Assignee: Electron Optical Research and Technology Corporation,Fremont, Calif.

22 Filed: Dec. 12, 1973 211 App]. No.: 424,159

[51] Int. Cl G01n 21/26; GOln 23/12 [58] Field of Search 250/311, 439,440, 442, 250/444, 457, 491

[56] References Cited UNITED STATES PATENTS 2,472,316 6/1949 Rennie250/311 [11] 3,885,157 51 May 20, 1975 2,499,019 2/1950 Dornfeld 250/4422,655,601 10/1953 Verhoeff 250/31 1 3,643,091 2/1972 Lucas 250/4423,778,62l 12/1973 Mikajiri 250/311 3,795,808 3/1974 Knights et al 250/311 FOREIGN PATENTS OR APPLICATIONS 895,636 1 H1953 Germany 250/440Primary ExaminerSaxfield Chatmon, Jr. Attorney, Agent, or Firm-CharlesL. Botsford [57] ABSTRACT A device containing and providing selectionbetween a plurality of electron beam processing units is located in thevacuum chamber of a microscope, so that the latter can be used in a widevariety of applications without breaking the vacuum.

18 Claims, 4 Drawing Figures FIG.3

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J r VH0 ELECTRON BEAM IMAGE PROCESSING DEVICE BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to a devicefor a method of multiple analysis of corpuscular rays, such as electronbeams. In particular, this invention relates to a device containing, andproviding selection between, a plurality of electron beam processingunits for use in transmission electron microscopy.

2. Description of the Prior Art Transmission electron microscopy enablesvisual examination to be made of structures too fine to be resolved withordinary, or light, microscopes, and thus has become an essentialresearch tool in such fields as biology, chemistry and metallurgy.

Briefly, the transmission electron microscope comprises a light" sourcesupplying a beam of electrons of uniform velocity, a condenser lens forconcentrating the electrons on a specimen, a specimen stage fordisplacing the specimen which transmits the electron beam, an objectivelens, several projector lenses, and a fluorescent screen that receiveselectrons and emits corresponding light rays to provide an image.Electrons are strongly scattered by all forms of matter including air,so that the entire microscope is evacuated to about millimeters ofmercury (that is, 10 atmospheric pressure).

In the prior art, several approaches have been used to process electronbeams after they leave the specimen stage of an electron microscope.One, mentioned above, comprises a fluorescent screen that receiveselectrons and produces a visual image. A fluorescent screen projects abright, usuable image provided that a large number of incident electronsare available at the screen.

Another approach is used when the large number of electrons needed atthe fluorescent screen for a bright image would damage or detrimentallyaffect a specimen located in an earlier stage of the microscope. A lownumber of electrons are used at the specimen stage, which are thenincreased after the specimen stage to a large number by use ofmulti-channel electron multipliers located between the specimen stageand the fluorescent screen. A multi-channel electron multiplierfunctions to increase greatly the number of electrons in a beam passingtherethrough without distorting the electron pattern. When the increasednumber of electrons reach the fluorescent screen, a bright usuable imageis produced. Use of a low number of electrons at the specimen stage thusprevents damage to the specimen, while use of the multiplier allows abright image to be obtained from the screen.

Still another approach is used when it is desirable to determine thenumber of electrons per unit area in a beam, that is, the electrondensity. An electron detector is placed before or after the fluorescentscreen, which indicates the density as an image is produced by thescreen.

As mentioned above, the chamber of the electron microscope is a vacuumto avoid scattering of electrons. Keeping a vacuum in the chamber makesit difficult to change easily an electron-beam processing unit in themicroscope. As a consequence, use of the microscope is limited toapplications compatible with the processing unit already locatedtherein. For other applications,

another microscope must be used, or else the vacuum in the firstmicroscope must be broken in order to change the processing unit, andthe chamber must then be re-evacuated. Either way is undesirable.Therefore, a device and method are needed that allow selection betweenvarious electron-beam processing units for use in a single electronmicroscope, without affecting its vacuum.

SUMMARY OF THE INVENTION The device containing, and method for selectingbetween, a plurality of electron-beam processing units overcomes theabove-mentioned disadvantages of the prior art because, according to theinvention, a number of different processing units are located in thechamber of a single microscope at the same time, and selection is madebetween the units without affecting the vacuum in the chamber. Briefly,the device of the invention comprises a movable platform located in thechamber and a lever mechanically coupled thereto, the lever extendingoutside the chamber. A plurality of electronbeam processing units aremounted on the movable platform and are selectively aligned by use ofthe lever. A deflection apparatus is also provided so that the electronbeam can be selectively deflected at various angles.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified cross-sectionalview of a portion of the chamber of an electron microscope modified tocontain the movable platform located therein, the lever mechanicallycoupled to the platform and extending outside the chamber, and theplurality of electronbeam processing units mounted on the platform.

FIG. 2 is a simplified two-dimensional top view of three electron-beamprocessing units mounted on the platform within the microscope chamber.

FIG. 3 is a simplified schematic drawing of circuitry for a switch tocontrol deflection of electron beams.

FlG. 4 is a simplified two dimensional top view of a portion of achamber of an electron microscope moditied to contain an alternativeembodiment of the movable platform.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, the devicefor multiple analysis of corpuscular rays, such as electron beams,comprises a chamber 1 having walls 2 enclosing space that is relativelydevoid of matter, such as a vacuum. Suitably, the space 15 evacuated tobelow 10 millimeters of mer- 'Y (H)? atmospheric pressure). Theevacuated space avoids unwanted scattering of electrons, which arecaused by collisions between electrons and particles m cluding air inthe atmosphere. Preferably, chamher 1 IS a portion of a microscope, suchas a transmission electron microscope, and is located after the specimenstage thereof. An Opening 3 is provided to allow an electron beam toenter chamber 1 from another portron of the microscope. Another opening4 provides for external viewing of a portion of the contents of chamberL SuItabIy, opening 4 is covered by a transparent material 5, such asglass or clear plastic, that allows retentlon of the vacuum seal inchamber 1.

A movable platform, such as turntable 10, is located within chamber 1.Preferably, turntable 10 is mounted so as to provide rotational movementabout an axis. A

lever 11 extends outside of chamber 1 and is mechanically coupled to theturntable 10 by means of torus l2. Lever 11 provides external control ofthe position of turntable 10 in chamber 1. Mounted on turntable H] are aplurality of electron-beam processing units. For example, one processingunit on turntable l comprises a fluorescent screen 20 (shown in FIG. 2).Fluorescent screen 20 functions in a manner similar to that of a cathoderay tube, that is, screen 20 receives electrons on one side and emitscorresponding light rays from the other side thereof. Screen 20comprises a suitable fluorescent material well known in the art andhereinafter is referred to as a phosphor screen. Phosphor screen 20 isaligned between openings 3 and 4 of chamber 1 by use oflever 11, so thatan electron beam entering opening 3 strikes one side of screen 20 and animage on the other side thereof corresponding to the electron pattern isviewed through opening 4. Phosphor screen 20 produces good images whenthe energy of electrons in the beam is in the range of 50 to 200kiloelectron volts, and when the electron intensity is in the range ofl0 to lO amperes per square centimeter.

Another example of an electron-beam processing unit located in turntablecomprises a plurality of electron multipliers 30 and 31 located over aphosphor screen 32 (see FIGS. 1 and 2). Preferably, each electronmultiplier comprises an array of cylindrical channels or tubes formed ofan insulative material, such as glass. A high resistive coating havingsecondary emissive effects is located on the inside of each channel ortube. For example, the coating resistance is about 1,000 megohms persquare, and the coating material comprises tin oxide or antimony oxide.The diameter of each tube is relatively small compared to its length, sothat electrons entering the tube impinge upon the resistive coating,causing secondary emission and multiplication of electrons.

Preferably, the channels or tubes in multipliers 30 and 31 are tilted ata small angle from the direction of the electron beam. For example, theangle of tilt of the channels in multiplier 30 is 8 in a clockwisedirection from the path of the electron beam, and the angle of tilt inmultiplier 31 is about 8 counterclockwise from the electron beam path.The use of the channels or tubes tilted at a small angle increases thenumber of times electrons travelling therein collide with the highresistive coating, and thereby increases the secondary emission effects.

The ends of the channels or tubes on one side of an array areelectrically connected to each other and to a lead, such as lead 35 formultiplier 30 (see FIG. I). Suitably, lead 35 comprises a thin metalstrip or film of conductive material. The ends of the channels or tubeson the other side of the array are electrically connected to each otherand to a lead, such as lead 36, for multiplier 30. An accelerating fieldacross the channels or tubes can be provided by applying the propervoltages to leads 35 and 36. Leads 37 and 38 provide electricalconnections respectively to the two sides of the array of channels ortubes of multiplier 31. Electrical insulation between leads 36 and 37 isprovided by a thin insulation material 39, such as mylar. Suitably, thearrays are supported securely above the phosphor screen 32 by posts 40,which are also of an insulating material, such as ceramic. An externalvoltage source is coupled to electrical leads 35 to 38 and screen 32 byuse of conductive wires 4] to 45 that extend from leads 35 to 38 andscreen 32 through the mid portion of turntable l0 and torus 12 to anexternal source.

Still another example of an electron-beam processing unit comprises aphosphor screen with a small hole 51 extending completely therethrough,the screen 50 mounted on turntable 10. Hole 51, for example, has adiameter of about 3 millimeters. Underneath screen 50 and aligned withhole 51 is an electron multiplier 53. Unlike multipliers 30 and 3],multiplier 53 has a single channel. The lining of the channel ofmultiplier 53 comprises a resistive coating. When incoming electronsimpinge upon the coating, secondary emission effects occur, resulting inelectron multiplication that is proportional to the number of electronsentering the multiplier. An ammeter capable of indiating very low current values, such as in the picoampere range, can be electricallycoupled to the output of multiplier 53 to detect electrical impulsesgenerated when electrons have passed through hole 51 and enteredmultiplier 53. The magnitude of a pulse is proportional to the number ofelectrons passing through hole 51.

Conductive wires 55 and 56 extend through the mid portion of torus l2and turntable l0 and are electrically connected to electron multiplier53 and phosphor screen 50 respectively, thereby providing connections toan external voltage source.

An electron beam striking one side of screen 50 results in the imageappearing on the other side thereof, while at the same time a portion ofelectrons in the beam pass through hole 51 and enter multiplier 53,thereby allowing determination of electron density at the same time theimage is being viewed.

Referring to FIG. 1, spaced deflecting coils or plates 60 and 61 areprovided for deflecting thet incoming electron beam as it enters throughopening 3. The deflecting elements may be electrostatic orelectromagnetic. For deflection in two directions, such as X- and Ydirections, a pair of spaced coils is provided, one pair for eachdirection. The degree of deflection in each direction is determined bythe magnatude of the potential applied to a selected pair of deflectioncoils. Spaced electrical leads 63 and 64, coupled respectively toelectrical terminals of deflectors 60 and 61, extend outside the chamberto enable application of voltage potentials to deflectors 61 and 62 froman external source.

An insulating material, such as TorrSeal" or equivalent, is provided atthe location where the leads 63 and 64 pass through the chamber wall, inorder to protect the vacuum in the chamber.

A multiposition switch, such as switch as shown in FIG. 3, along withthe circuit components, is provided to selectively control the magnitudeof the potential applied to deflectors 60 and 61, and thereby controlthe various degrees of deflection in one direction. Each of fourterminals through 78 of multiposition switch 70 is electrically coupledvia resistors through 88 to a center tap of one of four voltage dividers81 through 84. Resistors 85 through 88 ensure linear deflection uponadjustment of the center tap. The output from the center arm 71 ofswitch 70 is electrically coupled via electrical leads 63 and 64 todeflectors 60 and 61 in the microscope chamber, indicated symbolicallyin FIG. 3 as coil 61. The source of the voltage potential, for example,can be a direct-current power supply 90 coupled across voltage dividers81 through 84 by resistors 91 and 92. Preferably, the center arm 71 ofswitch 70 is connected to a timer (not shown), which periodically movesarm 71 through each of the four terminals 75 through 78, therebychanging the potential on coil 61 and controlling the degree ofdeflection of an incoming electron beam in chamber 1. Switch 70 enablesone to determine the electron density of four different portions of thebeam. Another switch is provided for shifting the beam in anotherdirection. such as the Y- direction. If desired, a multilevel switch canbe used for shifting the' beam in various directions at the same time.

As mentioned above, the entire chamber 1 is sealed to preserve theintegrity of the vacuum therein. Suitably, the sealing means comprises arubber or viton O- ring seal 100 (FIG. 1) at each place where portionsof the chamber come together. In addition, a cylinder may be fastened tothe chamber wall 102 in the vicinity of the torus 12 in order tocompress the O-ring seal against the torus 12 and prevent any leakage ofair into the chamber, especially during axial rotation of the torus 12.

Referring to FIG. 4, an alternative embodiment of the movable platformprovides for longitudinal movement, rather than rotational. Platform 110is moved longitudinally in chamber 111 by means of a gear mechanism 112and 113. Gear 113 is mechanically coupled to external lever 114 bymember 115. Rubber or viton O-ring seals 116 are provided to maintainthe vacuum in the chamber. Mounted on platform 110 are various electronbeam-processing units similar to those located on turntable 10 ofFIG. 1. For example, one processing unit comprises a phosphor screen 20.Another unit comprises a phosphor screen 32 with micro channel electronmultipliers 30 located thereover. Still another unit comprises aphosphor screen 50 with a small hole 51 extending therethrough toaccommodate an electron detector located thereunder. As desired,platform 110 can also contain an empty hole or leaded plate 120,particularly in applications where no special processing unit isrequired.

While the invention has been described with refer ence to particularembodiments, it includes numerous other modifications, which will beobvious to one skilled in the art.

I claim:

1. Device for analysis of corpuscular rays, such as an electron beamafter the beam has left the specimen stage of a transmission electronmicroscope, the device comprising:

a chamber having walls enclosing a space relatively devoid of matter, aportion of the chamber adapted to admit incoming corpuscular rays, suchas an electron beam;

a plurality of spaced electron-beam processing units located within thechamber, the units comprising:

a first processing unit comprising:

a phosphor screen having a relatively small hole extending through aportion thereof; and,

a single channel electron multiplier aligned with the hole, with thescreen located in front of the multiplier relative to an incomingelectron beam;

a second processing unit comprising:

a plurality of spaced multichannel electron multipliers; and

a phosphor screen, with the multipliers located in front of the screenrelative to an incoming electron beam;

a third processing unit comprising a phosphor screen:

means for selecting a processing unit and aligning said unit with anelectron beam in the chamber; and

means for selectively applying voltage potentials to a 5 selectedprocessing unit.

2. Device 'of claim 1 wherein said means for selecting and aligning aprocessing unit comprises a moveable platform within which saidprocessing units are mounted, and a lever mechanically coupled to theplat- IO form and extending outside the chamber.

3. Device of claim 2 wherein the lever is mechanically coupled bya gearmechanism, and the platform has longitudinal movement.

4. Device of claim 1 wherein said chamber is a portion of an electronmicroscope.

5. Device of claim 2 wherein the moveable platform comprises a rotatableturntable.

6. Device of claim 1 wherein said voltage potential applying meanscomprises a plurality of spaced electri cal leads electrically coupledbetween an external power source and electrical terminals of processingunits within the chamber.

7. Device of claim 1 further defined by a portion of one wall of thechamber comprising transparent material, so that an image produced by anelectron-beam processing unit can be viewed external to the chamber.

8. Device of claim 1 further defined by a deflection means located alonga portion of the chamber adapted to admit incoming electron beams, andmeans for selectively applying voltage potentials to the deflectionmeans.

9. Device of claim 8 wherein the deflection means comprises a pluralityof spaced coils.

10. Device of claim 8 wherein the deflection means comprises a pluralityof spaced conductive plates.

11. Device of claim 8 wherein the voltage potential applying meanscomprises spaced leads electrically coupled between an external powersource and electrical terminals of the deflection means.

12. Device of claim 11 further defined by a multiposition switch locatedoutside the chamber, and having output terminals electrically coupled tothe electrical leads, so that when potentials of different magnitudesare applied to the input terminals of the switch, the position of theswitch controls the potential applied to the deflection means.

13. Device of claim 12 further defined by a timer coupled to the switchto move periodically the switch through each of its positions.

14. Method of selecting between electron beam processing units for usein an electron microscope without breaking the vacuum in the chamberthereof, the steps comprising:

modifying a portion of the microscope chamber;

mounting a plurality of electron beam processing units onto a movableplatform having a lever me chanically coupled thereto;

inserting a movable platform into the modified portion of the chamber sothat the lever extends outside the chamber; and,

moving the lever so as to align a processing unit with an incomingelectron beam.

15. An electron image processing device for use in an 6 electron beaminstrument, the device comprising:

a microdensitometer unit;

an image intensifier unit;

a transmission phosphor screen unit; and,

ers; and.

a phosphor screen, with the multipliers located in front of the screenrelative to an incoming electron beam.

18. A microdensitometer device comprising:

a phosphor screen having a relatively small hole extending through aportion thereof; and,

a single channel electron multiplier aligned with the hole. with thescreen located in front of the multiplier relative to an incomingelectron beamv It It l

1. Device for analysis of corpuscular rays, such as an electron beamafter the beam has left the specimen stage of a transmission electronmicroscope, the device comprising: a chamber having walls enclosing aspace relatively devoid of matter, a portion of the chamber adapted toadmit incoming corpuscular rays, such as an electron beam; a pluralityof spaced electron-beam processing units located within the chamber, theunits comprising: a first processing unit comprising: a phosphor screenhaving a relatively small hole extending through a portion thereof; and,a single channel electron multiplier aligned with the hole, with thescreen located in front of the multiplier relative to an incomingelectron beam; a second processing unit comprising: a plurality ofspaced multichannel electron multipliers; and a phosphor screen, withthe multipliers located in front of the screen relative to an incomingelectron beam; a third processing unit comprising a phosphor screen:means for selecting a processing unit and aligning said unit with anelectron beam in the chamber; and means for selectively applying voltagepotentials to a selected processing unit.
 2. Device of claim 1 whereinsaid means for selecting and aligning a processing unit comprises amoveable platform within which said processing units are mounted, and alever mechanically coupled to the platform and extending outside thechamber.
 3. Device of claim 2 wherein the lever is mechanically coupledby a gear mechanism, and the platform has longitudinal movement. 4.Device of claim 1 wherein said chamber is a portion of an electronmicroscope.
 5. Device of claim 2 wherein the moveable platform comprisesa rotatable turntable.
 6. Device of claim 1 wherein said voltagepotential applying means comprises a plurality of spaced electricalleads electrically coupled between an external power source andelectrical terminals of processing units within the chamber.
 7. Deviceof claim 1 further defined by a portion of one wall of the chambercomprising transparent material, so that an image produced by anelectron-beam processing unit can be viewed external to the chamber. 8.Device of claim 1 further defined by a deflection means located along aportion of the chamber adapted to admit incoming electron beams, andmeans for selectively applying voltage potentials to the deflectionmeans.
 9. Device of claim 8 wherein the deflection means comprises aplurality of spaced coils.
 10. Device of claim 8 wherein the deflectionmeans comprises a plurality of spaced conductive plates.
 11. Device ofclaim 8 wherein the voltage potential applying means comprises spacedleads electrically coupled between an external power source andelectrical terminals of the deflection means.
 12. Device of claim 11further defined by a multiposition switch located outside the chamber,and having output terminals electrically coupled to the electricalleads, so that when potentials of different magnitudes are applied tothe input terminals of the switch, the position of the switch controlsthe potential applied to the deflection means.
 13. Device of claim 12further defined by a timer coupled to the switch to move periodicallythe switch through each of its positions.
 14. Method of selectingbetween electron beam processing units for use in an electron microscopewithout breaking the vacuum in the chamber thereof, the stepscomprising: modifying a portion of the microscope chamber; mounting aplurality of electron beam processing units onto a movable platformhaving a lever mechanically coupled thereto; inserting a movableplatform into the modified portion of the chamber so that the leverextends outside the chamber; and, moving the lever so as to align aprocessing unit with an incoming electron beam.
 15. An electron imageprocessing device for use in an electron beam instrument, the devicecomprising: a microdensitometer unit; an image intensifier unit; atransmission phosphor screen unit; and, a moveable platform within whicheach of the units is mounted and spaced apart.
 16. Device of claim 15wherein the microdensitometer unit comprises: a phosphor screen having arelatively small hole extending through a portion thereof; and, a singlechannel electron multiplier aligned with the hole, with the screenlocated in front of the multiplier relative to an incoming electronbeam.
 17. Device of claim 15 wherein the image intensifier unitcomprises: a plurality of spaced multichannel electron multipliers; and,a phosphor screen, with the multipliers located in front of the screenrelative to an incoming electron beam.
 18. A microdensitometer devicecomprising: a phosphor screen having a relatively small hole extendingthrough a portion thereof; and, a single channel electron multiplieraligned with the hole, with the screen located in front of themultiplier relative to an incoming electron beam.